The neural crest is a transitory embryonic structure from which cells spread at an early developmental stage, migrate in the developing embryo and differentiate into several cell types. Many problems remain unsolved concerning the evolution of this structure. The normal fate of the cells which derive from the neural crest is not yet fully known and on the other hand it realizes an interesting system to study the mechanisms which control cell migration and differentiation. I have devised a stable biological cell marking system which can be applied in higher vertebrates and which we have used these last years to investigate the problem of crest cell migration and differentiation. Our purpose is to complete this work and to focus our effort especially on the following points: 1) The contribution of neural crest in head and neck morphogenesis, and in endocrine glands. 2) The factors controlling the pattern of crest cell migration through experiments performed both in vivo and in vitro. 3) The influence of cell interaction on the differentiation of neural crest cells.